The concentration increase of acid gas such as carbon dioxide (CO2), methane (CH4), hydrogen sulfide (H2S), carbonyl sulfide (COS) or the like in the air from the use of fossil fuel is causing global warming. In particular, reducing the concentration of carbon dioxide in the air has been actively discussed worldwide in various aspects since the Rio De Janeiro Environmental Conference in 1992.
Carbon dioxide capture and storage (CCS) technologies are isolating carbon dioxide discharged in large quantity from power plants, steel plants or cement plants from the air.
In particular, carbon dioxide capture in CCS technologies is considered a core technology that takes about 70% to about 80% of the overall costs, which may be classified into post-combustion technology, pre-combustion technology, and oxy-fuel combustion technology (refer to “Carbon Dioxide Capture and Storage Technology”, by Sang-do Park, Physics and Advanced Technologies, June, 2009).
Post-combustion technology is isolating carbon dioxide (CO2) produced from combustion of fossil fuel by absorbing or reacting the carbon dioxide (CO2) with various solvents. Pre-combustion technology is capturing carbon dioxide (CO2) in exhaust gas before combustion by pre-treating fossil fuel such as coal, for example, via gasification into carbon dioxide (CO2) and hydrogen (H2), and then isolating the carbon dioxide (CO2) from the mixed gas of carbon dioxide (CO2) and hydrogen (H2) or combusting the mixed gas. Oxy-fuel combustion technology is combusting fossil fuel with only pure oxygen instead of air, thereby to easily capture carbon dioxide (CO2). Post-combustion technology of the above-described technologies is currently most widely used.
Post-combustion technology is the most easy to apply with existing carbon dioxide sources, which separates carbon dioxide by absorbing or desorbing carbon dioxide with absorbent, focusing on performance improvement of the absorbent and process improvement therefor. This post-combustion technology includes wet absorption and dry absorption technologies that are currently in commercial use to supply carbon dioxide required for automatic welding or producing urea fertilizer or carbonated drink. Wet absorption technology may have higher efficiency than dry absorption technology.
A typical wet absorption process is a capture process using amine-based absorbent. This process has been used in a modification process involved in petrochemical processes with ensured technical reliability, but still needs further improvement in terms of absorbent performance and process improvement in order to be applicable with flue gas including various contaminants. As a process using amine-based absorbent, a chemical absorption process using an alkanolamine absorbent that includes both amine and hydroxyl groups bound to an alkyl group may be performed using a system equipped with an absorption tower for selectively absorbing carbon dioxide from inflow gas with the absorbent, a recycling tower (hot recycling tower) for processing the carbon dioxide-absorbed absorbent to regenerate the initial absorbent free of carbon dioxide for recycling, and other accessory equipments.
Monoethanolamine (MEA), as a most widely used amine-based absorbent, has alkaline properties due to unshared electrons in amine groups, which may cause acid-base neutralization reaction with acidic carbon dioxide. Furthermore, salts (carbamate or bicarbonate) as reaction products may be decomposed at a temperature of about 110° C. to about 130° C. to regenerate the absorbent. The ability to absorb carbon dioxide (CO2) and the absorption rate of an absorbent may vary according to structural characteristics of amines used in the absorbent.
A carbon dioxide absorption process may be performed at about 40° C. to about 50° C., while a recycling process may be performed at about 110° C. to about 130° C. Accordingly, part of the absorbent may vaporize during the recycling process and be discharged together with carbon dioxide. In this regard, there is a need for preheating technologies to reduce the heat duty of such as a cooler and condenser for cold condensation and a reboiler in the recycling process.
Korean Patent No. 0983677 relates to a system and method of absorbing and separating acid gas, wherein using steam generated in a boiler as a heat source for recycling absorbent is disclosed. However, using the generated steam only for absorbent recycling still has limitations.
Therefore, there is a need for the development of technologies to reduce the energy consumption in heating and cooling of the recycling process.